U.S. patent application number 12/597720 was filed with the patent office on 2010-06-03 for multiple-spot laser refractive ophthalmic surgery.
This patent application is currently assigned to Carl Zeiss Meditec AG. Invention is credited to Mark Bischoff, Marco Hanft, Gregor Stobrawa, Martin Wiechmann, Lars Christian Wittig.
Application Number | 20100137849 12/597720 |
Document ID | / |
Family ID | 39777476 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100137849 |
Kind Code |
A1 |
Hanft; Marco ; et
al. |
June 3, 2010 |
MULTIPLE-SPOT LASER REFRACTIVE OPHTHALMIC SURGERY
Abstract
An apparatus for material processing by laser radiation,
including a laser source which emits a processing beam, and a beam
path for focusing and scanning, the beam path focusing the
processing beam into a processing volume and shifting the position
of the focus therein. A beam splitting device generates several
foci in the processing volume and the beam splitting device splits
the processing beam up into a primary beam and at least one
secondary beam and leaves the cross section of the beam in a pupil
plane of the beam path unchanged during said division and
introduces an angle of separation between the primary and secondary
beams, so that these beams expand in the beam path in directions
which differ by the angle of separation.
Inventors: |
Hanft; Marco; (Jena, DE)
; Wiechmann; Martin; (Jena, DE) ; Bischoff;
Mark; (Bad Berka, DE) ; Stobrawa; Gregor;
(Jena, DE) ; Wittig; Lars Christian; (Jena,
DE) |
Correspondence
Address: |
PATTERSON THUENTE CHRISTENSEN PEDERSEN, P.A.
4800 IDS CENTER, 80 SOUTH 8TH STREET
MINNEAPOLIS
MN
55402-2100
US
|
Assignee: |
Carl Zeiss Meditec AG
Jena
DE
|
Family ID: |
39777476 |
Appl. No.: |
12/597720 |
Filed: |
April 22, 2008 |
PCT Filed: |
April 22, 2008 |
PCT NO: |
PCT/EP08/03221 |
371 Date: |
January 13, 2010 |
Current U.S.
Class: |
606/5 |
Current CPC
Class: |
G02B 27/0977 20130101;
B23K 26/0604 20130101; G02B 27/0944 20130101; A61F 2009/00872
20130101; A61F 9/008 20130101; G02B 26/101 20130101; B23K 26/067
20130101; B23K 26/0608 20130101; A61F 9/0084 20130101; B23K 26/0676
20130101; A61F 9/00827 20130101; G02B 27/0905 20130101 |
Class at
Publication: |
606/5 |
International
Class: |
A61F 9/01 20060101
A61F009/01; A61B 18/20 20060101 A61B018/20 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2007 |
DE |
10 2007 019 812.6 |
Apr 26, 2007 |
US |
60914182 |
Claims
1-11. (canceled)
12. An apparatus for refractive ophthalmic surgery by laser
radiation, said apparatus comprising: a source of radiation which
emits a processing beam; a beam path for focusing and scanning,
said beam path focusing the processing beam into a cornea of an eye
and shifting a position of a focus therein; a beam splitting device
that generates several foci in the cornea, wherein the beam
splitting device divides the processing beam into a primary beam
and at least one secondary beam and leaves a cross section of the
beam unchanged during said division, so that the primary and
secondary beams have the same cross section as the processing beam
which is incident on the beam splitting device; wherein the
beam-splitting device introduces an angle of separation between the
primary and secondary beams, so that the primary and secondary
beams expand in the beam path in directions which differ by the
angle of separation; and further comprising a contact glass which
induces a pre-defined geometric boundary surface at the cornea.
13. The apparatus as claimed in claim 12, wherein the beam
splitting device does not have a focusing effect.
14. The apparatus as claimed in claim 12, wherein the beam
splitting device is arranged close to a pupil in the beam path.
15. The apparatus as claimed in claim 12, wherein the beam
splitting device is arranged anterior to scanning elements.
16. The apparatus as claimed in claim 12, wherein the beam
splitting device can be activated and de-activated.
17. The apparatus as claimed in claim 12, wherein the beam
splitting device comprises a diffractively working element.
18. The apparatus as claimed in claim 17, wherein said element is a
phase grating.
19. The apparatus as claimed in claim 12, wherein the beam
splitting device comprises an element which comprises wedges and
planar plates.
20. The apparatus as claimed in claim 12, wherein the beam
splitting device rotates the at least one secondary beam around the
primary beam.
21. The apparatus as claimed in claim 20, further comprising a
control unit, which controls the rotation synchronously with the
focus position adjustment.
22. The apparatus as claimed in claim 20, wherein the beam
splitting device comprises a rotating grating or a rotating
segmented plate.
23. The apparatus as claimed in claim 21, wherein the beam
splitting device comprises a rotating grating or a rotating
segmented plate.
24. The apparatus as claimed in claim 20, wherein the beam
splitting device separately directs the at least one secondary beam
to a scanning device which deflects the at least one secondary beam
in a controlled manner before the beam splitting device
superimposes the primary beam again on the thus-deflected at least
one secondary beam.
25. The apparatus as claimed in claim 21, wherein the beam
splitting device separately directs the at least one secondary beam
to a scanning device which deflects the at least one secondary beam
in a controlled manner before the beam splitting device
superimposes the primary beam again on the thus-deflected at least
one secondary beam.
Description
PRIORITY CLAIM
[0001] The present application is a National Phase Entry of PCT
Application No. PCT/EP2008/003221, filed Apr. 22, 2008, which
claims priority to U.S. Provisional Application No. 60/914,182,
filed Apr. 26, 2007, and German Application Number 102007019812.6,
filed Apr. 26, 2007, the disclosures of which are hereby
incorporated by reference herein in their entirety.
FIELD OF THE INVENTION
[0002] The invention relates to an apparatus for refractive
ophthalmic surgery by laser radiation, said apparatus comprising a
laser source which emits a processing beam, and a beam path for
focusing and scanning, said beam path focusing the processing beam
into the cornea of an eye and shifting the position of the focus
therein, a beam splitting device being provided to generate several
foci in the cornea.
BACKGROUND
[0003] The processing of material by laser radiation is known. A
particular application for processing transparent materials, where
a processing effect is obtained by a non-linear interaction of the
laser radiation with the per se transparent material, is refractive
ophthalmic surgery. For surgery, the laser radiation is focused
into the eye's cornea, and the focus is shifted along a cut surface
to be generated.
[0004] Of course, the processing time depends on how long the
interaction in the focus lasts. An acceleration can be achieved by
working with several focus spots at a time.
[0005] Therefore, EP 1279386 A1, which discloses an apparatus of
the above type, describes how to shorten the treatment time by
multiplying the spots, allowing the simultaneous processing of
larger partial areas. The presented solution has several
disadvantages. According to FIG. 4 of this publication, a beam 38
is split into partial beams 44 a . . . c by lenses 42 a . . . c.
The diameter the beams 44 a . . . c have directly at the lenses 42
a . . . c is smaller than the diameter of the beam 38. This is a
disadvantage, because a smaller beam cross section at the lenses 42
a . . . c causes the beams 44 a . . . c to be have an inferior
focusing ability as compared to the beam 38. That is, either larger
spots result or the cross sections have to be adapted. After
interaction of the near-parallel beam 38 with the lenses 42 a . . .
c, convergent beams 44 a . . . c form so that foci are located
within the optical system. This is disadvantageous because it may
cause high field strengths with undesired effects within the
optical system, for example an energy-consuming optical
breakthrough at a position in the optical beam path other than the
target position in the material to be treated. Moreover, any
focusing element always generates a need for adaptation to the
subsequent optics, e.g. by collimation. This accordingly results in
additional complexity.
[0006] Also, in the state of the art, a scanning element is
positioned directly in the intermediate image, i.e. conjugated to
the actual processing plane. Although the beams would be deflected
when using a galvanometer scanner, there would be no change of
location. Therefore, the spots would rest in the processing volume
despite any deflections of the galvanometer scanner. Further, the
design according to DE 60208968 additionally uses an active mirror
having 40,000 active facets, which is complex and expensive.
[0007] A further problem of the known arrangement is that a fixed
offset between the individual spots is generated anterior to the
scanner. A spiral scan will then result in points of intersection
between the spot paths in the processing volume. This leads to a
non-concentric course of the paths, especially for a small number
of spots.
SUMMARY OF THE INVENTION
[0008] Therefore, it is an object of the invention to provide an
apparatus for refractive ophthalmic surgery by laser radiation of
the above-mentioned type such that several focus spots can be used
without the above-described disadvantages.
[0009] According to the invention, this object is achieved by an
apparatus for refractive ophthalmic surgery by laser radiation,
said apparatus comprising a laser source, which emits a processing
beam, and a beam path for focusing and scanning, which beam path
focuses the processing beam into the cornea of an eye and shifts
the position of the focus therein, a beam splitting device being
provided to generate a plurality of foci in the processing volume,
which beam splitting device divides the processing beam into
primary and secondary beams and leaves the cross section of the
beam unchanged during dividing, so that the primary and secondary
beams have the same cross section as the processing beam which is
incident on the beam splitting device, wherein said beam splitting
device introduces an angle of separation between the primary and
secondary beams, so that the primary and secondary beams extend in
the beam path in directions which differ by the angle of
separation, and wherein a contact glass is provided, which induces
a predefined geometric interface at the cornea.
[0010] It is particularly easy to make the beam splitting device
leave the cross section unchanged, preferably in the pupil, if the
device itself is located in or near the pupil of the beam path.
Further, the beam splitting device preferably does not have a
focusing effect. It is also convenient to arrange the beam
splitting device anterior to scanning elements in the beam
direction.
[0011] FIG. 15 shows how the term "closeness to the pupil" is
understood in connection with the present invention. It shows an
axial beam 40 which is characterized by its peripheral rays 41 and
a main ray 42. The aperture of the axial beam 40 is defined by its
peripheral rays 41. Further, a field beam 43 is depicted by way of
example. A reference plane 44 is located near a pupil plane 45, as
long as, for all field beams 43, the intersection point 47 of a
main ray 46 and the reference plane 44 is located within the
aperture of the axial beam. Thus, a plane's closeness to the pupil
is characterized in that the points of intersection where all the
field beam main rays pass through the plane are located within the
axial beam's aperture which is defined by the peripheral rays.
[0012] In order to enable switching between single-spot and
multiple-spot processing, it is convenient to provide the effect of
the beam splitting device such that it can be switched on and off,
for example by a mechanical system which disengages the beam
splitting device from the beam path or bypasses it in the beam
path.
[0013] For splitting, the beam splitting device may comprise a
diffractively effective element, which may be provided as a phase
grating, for example. Said phase grating preferably also comprises
means for distributing the radiation intensity of the incident
processing beam as uniformly as possible to a limited number of
main maxima.
[0014] Particularly uniform distribution of the radiation intensity
with the possibility of generating a very great number of secondary
beams is possible by the use of a beam splitting device which
comprises elements consisting of wedges and planar plates, e.g. in
the form of a segmented plate, whose segments alternate between
different wedges and planar plate elements.
[0015] In the case of circular deflection of the position of the
focus in the processing volume, the multiplicity of generated spots
may cause intersecting of the respective, e.g. circular, paths on
which the foci are shifted. In order to avoid this, it is
convenient to control the angle of separation as a function of the
target position of the primary spot. A particularly simple
realization of this further embodiment is a beam splitting device
which rotates the at least one secondary beam about the primary
beam in an adjustable manner. For control, an additional further
embodiment may then provide a control unit which controls the
rotation synchronously with the shifting of the focus position.
This prevents intersecting of paths of the spots of the primary and
secondary beams. For example, the spots move on concentric circular
paths.
[0016] It will be appreciated that the features mentioned above and
those yet to be explained below can be employed not only in the
indicated combinations, but also in other combinations, or alone,
without departing from the scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be explained in more detail below, by way
of example and with reference to the enclosed drawings, which also
disclose features of the invention and wherein:
[0018] FIG. 1 depicts the beam path for a treatment apparatus using
several processing spots;
[0019] FIG. 2 depicts a further embodiment of the apparatus of FIG.
1;
[0020] FIG. 3 depicts a further embodiment of the apparatus of FIG.
1;
[0021] FIG. 4 depicts a representation similar to FIG. 1 of a
particular construction of the beam splitting element;
[0022] FIGS. 5a-d depict representations explaining the
construction and function of the beam splitting element of FIG.
4;
[0023] FIG. 6 depicts paths of the multiple-spot foci generated in
the processing volume by the treatment apparatus of FIG. 4;
[0024] FIG. 7 depicts a representation similar to FIG. 6 for seven
spots;
[0025] FIG. 8 depicts a representation similar to FIG. 4, but with
a differently designed beam splitting element;
[0026] FIGS. 9a-c depict representations explaining the
construction of the beam splitting elements of FIG. 8;
[0027] FIG. 10 depicts a treatment apparatus similar to that of
FIG. 1, but with a controllable beam splitting element;
[0028] FIG. 11 depicts a representation similar to that of FIG. 6
for the treatment apparatus of FIG. 8;
[0029] FIGS. 12a-b depict drawings relating to the construction and
function of the beam splitting element of FIG. 10;
[0030] FIG. 13 depicts a representation similar to that of FIG. 6
for a modification of the treatment apparatus of FIG. 10;
[0031] FIG. 14 depicts a schematic drawing of a further beam
splitting element for a treatment apparatus with analogy to FIG. 1,
and
[0032] FIG. 15 depicts a schematic drawing explaining the term
"proximity to the pupil".
DETAILED DESCRIPTION
[0033] FIG. 1 shows a laser-surgical system for
refraction-correcting treatment of the human eye. The system
comprises a source 1 of radiation, which may be provided, for
example, as a femtosecond laser, whose radiation is used to process
a material, which is the cornea of an eye 2 in the example
embodiment described herein. In order to obtain a defined
geometrical boundary surface or interface at the cornea 3, a known
contact glass 4 is placed on the cornea 3.
[0034] The source 1 of radiation provides a processing beam 5,
optionally by the use of optics 6 arranged posterior to the source
1 of radiation. An aperture stop 7 defines the cross section of the
beam and the pupil in the beam path that leads to the eye 2. Near
the aperture stop 7, i.e. near the pupil, there is a beam splitter
8, which divides the incident processing beam 5 such that a
secondary beam 9 is split off, which extends in a slightly
different direction to that of the primary beam 10 not being split
off. The cross section of the processing beam 5 is not changed
thereby. The angle of divergence or angle of separation between the
primary beam 10 and the secondary beam 9 is indicated by way of
example and is referred to by the reference numeral 11. Scanners
12, 13 arranged posterior to the beam splitter 8 deflect the
processing radiation in the beam path. Thus, foci 15a, 15b are
formed in the processing volume 2 by subsequently arranged focusing
optics 14.
[0035] Accordingly, the laser-surgical system comprises: a source 1
of radiation (e.g. fs laser), which emits the beam 5; the beam
splitter 8, which divides the processing beam into the primary beam
10 and one or more secondary beams 9; one or more scanning elements
12, 13 (for example, scanning mirrors) for deflection of the beams
8, 10; and focusing optics 14, which focus the beams 9, 10 into the
cornea 3 of the eye 2.
[0036] The source 1 of radiation is preferably a femtosecond laser
emitting fs pulses in the wavelength region of 700-1150 nm and over
a spectral width of +/-5 nm. The pulse duration is 10-900 fs.
Sources of this type are known and may also comprise pulse-shaping
devices in addition to the actual laser.
[0037] For a multiple focus to form, beam splitting is effected
near a pupil. A pupil is an image of an aperture stop 7, or the
aperture stop 7 itself. The aperture stop 7 defines the aperture of
the beams 5, 9, 10 which opening is used for imaging. The beam
splitter 8 generates an angular offset of the secondary beams 9
relative to the primary beam 10. This angle of separation 11 leads
to separate foci 15a, 15b in the processing volume posterior to the
scanning optics 12, 13, 14. It should be noted here that a great
number of alternative positions are possible to locate the beam
splitter 8, e.g. on the scanning mirrors 12, 13 themselves,
posterior to the scanning mirrors 12, 13 or even as part of the
focusing optics 14. The decisive factor is the closeness to the
pupil.
[0038] The beam splitter 8 deflects portions of the beam 5 into the
secondary beams 9. Following the splitter the primary 10 and
secondary beams 9 extend in slightly different directions; thus,
the angle of separation 11 is formed between the beams 9, 10. The
beam splitter 8 further has the property that the beam's cross
section remains unchanged. This leads to the particular advantage
that the aperture in the foci 15a, 15b remains unchanged and, thus,
the size of the foci 15a, 15b does not change. The complexity of an
otherwise required adaptation of aperture is dispensed with
completely. Also, no additional constructional space is needed
apart from the space for the splitter 8.
[0039] The beam splitter preferably does not have a focusing effect
and, thus, generates no intermediate foci. Thus, undesired effects,
such as optical breakthroughs within the system, are avoided.
[0040] The scanning elements are preferably galvanometer scanning
mirrors 12, 13, which deflect the beam(s) 9, 10 in adjustable
directions. Arranged following the scanners 12, 13 are the focusing
optics 14 through which the beams 9, 10 are focused into a therapy
volume (cornea) 2, where processing is effected. The multiple spots
15a, 15b are guided through the therapy volume by the scanners 12,
13 according to a predetermined path. The predetermined paths are
preferably spirals or lines.
[0041] Due to the particularly preferable circular paths or
circle-like paths (ellipses, spirals), fixed beam splitting
produces intersecting of the spot paths, which intersecting can be
avoided by closed-loop controlled or synchronized beam splitting,
as will be described later.
[0042] In order to selectively work without multiplication of the
spots, the effect of the beam splitter 8 can be optionally switched
off. The beam splitter 8 can be switched on and off in many
ways.
[0043] In FIG. 2 (elements in this and further Figures which
correspond to elements already explained are provided with the same
reference numerals and shall not be described again), the beam
splitter 8 itself is movable, for example. If its effect is
desired, it is pushed or folded into the beam path by means of an
apparatus. Moreover, it is also possible to bypass the beam
splitter 8. A stepped mirror arrangement 17 comprising mirrors
18-21 is provided for this purpose in the example of FIG. 3, said
arrangement 17 being movable as a whole or in parts. The mirrors 18
and 21 can be folded in and out of the beam path, for example. When
they are folded into the beam path, the stepped mirror arrangement
17 is active and the beam splitter 8 is bypassed. In order to
achieve a constant power density per spot in both single-spot
operation and multiple-spot operation, the power of the source 1 of
radiation is preferably adapted to the status of the beam splitter
8 (active or deactivated).
[0044] A diffractively working element (grating) is preferred for
the beam splitter 8. Referring to FIG. 4, a phase grating is
explained as an example of a specific set of parameters, for ease
of illustration. It is expressly pointed out that similar solutions
can be embodied also using other gratings and other sets of
parameters. In the construction of FIG. 4, the aperture stop has a
diameter of 15 mm. The phase grating has a period of 4.16 mm. This
leads to an angle of separation of 0.014.degree.. The focal length
of the focusing optics is 20 mm. A possible design of the phase
grating of the beam splitter 8 and its function are explained
hereinafter with reference to FIGS. 5a-c.
[0045] The beam splitter 8 is a binary phase grating, which leads
to beam splitting in different directions according to the grating
formula:
sin .alpha. = .+-. k .lamda. g ##EQU00001##
[0046] with .alpha. being the direction of the maxima, k being
orders, .lamda. being the wavelength and g being the grating
constant.
[0047] The separation between the foci is obtained approximately
according to
y'=f'tan .alpha..apprxeq.f'sin .alpha.
[0048] with y' being the focus position for the 0.sup.th order,
.alpha. being the direction of the maxima and f' being the focal
length of the focusing optics.
[0049] For a wavelength of, for example, 1040 nm, the +/-1.sup.th
orders are at +/-0.014 degrees relative to the 0.sup.th order.
Thus, posterior to the focusing optics, which have a focal length
of 20 mm, a deviation of 5 .mu.m results between the foci. Due to a
preferably provided groove shape of the grating, the major part of
the energy is diffracted into the 0.sup.th, the -1.sup.th and the
+1.sup.th order. The differences in intensity between the three
main maxima are minimal. Of course, other means are also possible
for this purpose. If the threshold for the optical breakthrough is,
for example, at 30% of the maximum intensity, only the 3 main
maxima will produce an optical breakthrough. Thus, the beam has
been tripled. FIGS. 5a-c show the pupil function and the intensity
distribution of a binary phase grating having a period of 4.16 mm,
a bar-space-ratio of 1:1, a phase amplitude of 2.015 rad and a
symmetric arrangement.
[0050] FIG. 5a shows the pupil function for the grating in the form
of an amplitude image 22 as well as a phase image 23. The
diffraction characteristics of this grating are illustrated in
FIGS. 5b and 5c. As can be seen, the main energy flows into the
0.sup.th order 24 as well as the +1.sup.th order 25 and as the
-1.sup.th order 26. FIG. 5b shows the intensity values as the peak
intensity for each order, normalized to the peak intensity of the
0.sup.th order. The plotting of the intensity I in FIG. 5c also
illustrates that only the first three main maxima carry radiation
sufficient for an optical breakthrough. Integral evaluation of the
peaks shows that a mere 16.35% of the radiation energy passes into
still higher orders of diffraction (2.sup.hd orders and above) and
is, thus, not available. Accordingly, the phase grating effectively
achieves splitting of the processing beam 5 into a primary beam 24
(corresponding to the 0.sup.th order) as well as two secondary
beams 25, 26 (corresponding to the +/-1.sup.th orders).
[0051] In the described embodiments, the beam splitter anterior to
the scanning mirrors 12, 13 causes a fixed offset, e.g. in the y
direction. If the scanners 12, 13 are controlled according to a
circular path for the 0.sup.th order, the image of FIG. 6 will
result in the target volume. The foci 15a, 15b move along circular
paths 27a, b, c whose centers are mutually offset.
[0052] In the case of such a fixed offset, a grating design is of
advantage which two-dimensionally generates more than 3 foci. This
can be achieved, for example, in that the primary beam is divided
by the beam splitter 8 in two spatial directions. Said splitting
may be effected by sequential splitting in two directions, which
are preferably orthogonal to one another, as achieved, for example,
by an arrangement of two diffraction gratings, which are rotated
relative to each other at 90.degree. about the beam axis. Since
these two diffractive elements are to be arranged at least
approximately in a position in the beam path that is optimal for
splitting (pupil or near the pupil), an arrangement of the two in
immediate spatial proximity to one another is preferred.
[0053] The focus image of an arrangement comprising 7 spots is
schematically shown as an example in FIG. 7. The individual spot
paths 27 intersect several times, forming a ring-like pattern. The
Figure shows the spot paths 27, with the intersection of the spot
paths 27 resulting from the fixed splitting being clearly visible.
The unfavorable effects of an intersection can be reduced by
greater distances between the individual spots 25, bearing in mind,
however, that all spots are located in one plane perpendicular to
the optical axis. This prerequisite has to be taken into account
when defining the separation distance. If two-dimensionally curved
cut surfaces (e.g. spheres) are to be cut, this will result in an
upper limit for the separation distance. In the case of a spherical
cut having a radius of curvature of 20 mm, the strictest criterion
occurs for points which are remote from the center. Depending on
the definition of the depth tolerance, a specific distance from the
center (e.g. 5 mm) will yield a maximum allowable separation
distance (of the group of spots generated, i.e. a sort of diameter
of the group of spots). This distance is, for example, 3 .mu.m for
a depth tolerance of 0.8 .mu.m, approximately 5 .mu.m for a depth
tolerance of 1.3 .mu.m, or 10 .mu.m for a depth tolerance of 2.6
.mu.m. A limitation to, for example, few .mu.m in the diameter of
the group of spots appears useful for applications.
[0054] In a further embodiment according to FIGS. 8 and 9 a-c, a
segmented element whose segments consist of glass strips is used as
the beam splitter 8. The strips are provided as wedges A and C or
as a planar plate B. An example is specifically dimensioned here.
However, it is expressly pointed out that other sets of parameters
also yield valuable solutions. Such sets can be found by a person
skilled in the art by modifying the parameters explained below.
FIG. 8 shows only the beams of segments A and B.
[0055] Each wedge A, C deflects a beam. For scanning optics having
a focal length of 20 mm and a distance of 5 .mu.m between the
spots, an angle of separation of 0.014.degree. results. This angle
is formed by wedges having a refractive index of n=1.5 and a wedge
angle of 1.72 angular minutes. In order to provide 3 beams
(-0.014.degree./0.degree./+0.014.degree.), the pupil can be
divided. For this purpose, wedge segments and segments of planar
plates are combined, as shown in FIGS. 9 a, b, c, which depict
lateral views of the individual elements (FIG. 9a) of the segmented
element (FIG. 9b) and a top view of the segmented element (FIG.
9c).
[0056] The above-explained variants with fixed beam splitting
generate a deflection anterior to the scanners 12, 13. This
deflection is fixed and causes a fixed offset. In this case, each
spot 15 for itself may move on a circular path, but the circular
paths are not concentric. In order to avoid this, a manipulator
unit realizes controlled beam splitting according to a further
embodiment. In this case, beam splitting is effected depending on
control signals from a control unit 28. Said control unit 28
realizes a synchronization between the scanners 12, 13 and a
manipulator unit 29 for the beam splitter 8, as shown in FIG.
10.
[0057] Offset control is effected as a function of the target
position of the primary spot and enables, for example, a spiral
scan without the paths intersecting. The primary and secondary
spots 15a, 15b move on concentric circular paths 27a, 27b having a
fixed path distance 30, as shown in FIG. 11.
[0058] The manipulator may preferably be provided as a rotary beam
splitter 8 according to FIGS. 12 a, b. As described above, the beam
splitter 8 may be a phase grating or a segmented plate. The
rotation of the beam splitter 8 is synchronized with the x and y
control of the scanners by the control unit, so that, as a result,
the secondary beams 9 rotate around the primary beam 10.
[0059] If the beam is split into three parts (e.g. by the phase
grating or the element consisting of wedge segments) and
appropriately synchronized, the spots will move concentrically
(FIG. 13).
[0060] In a further embodiment for a manipulator unit 32 according
to FIG. 14, manipulation of the secondary beam 9 is effected
separately. The primary beam 10 passes through the beam splitter 8
without manipulation. A splitter 31 separates a part of the
processing beam, said part forming the secondary beam 9 which is
subjected to manipulation (offset) in unit 32. The secondary beam 9
then gets the primary beam 10 superimposed by means of a further
splitter 33. Utilizing polarization allows to optimize separation
and superimposing with negligible losses. Two foci are generated.
This variant is realizable in a fixed manner and in a controlled or
synchronized manner.
[0061] The manipulator in unit 32 can be embodied in many ways,
e.g. as a mirror (stationary or scanning), a rotary wedge and/or a
pair of wedges which are rotated relative to each other for offset
adjustment.
* * * * *